Wafer level package having a pressure sensor and fabrication method thereof

ABSTRACT

A wafer level package having a pressure sensor and a fabrication method thereof are provided. A wafer having the pressure sensor is bonded to a lid, and electrical connecting pads are formed on the wafer. After the lid is cut, wire-bonding and packaging processes are performed. Ends of bonding wires are exposed and serve as an electrical connecting path. A bottom opening is formed on a bottom surface of the wafer, in order to form a pressure sensor path.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to wafer level packages, and, more particularly,to a wafer level package having a pressure sensor and a fabricationmethod thereof.

2. Description of Related Art

A pressure sensor uses pressure sensing elements to sense gas or liquidpressure. With the rapid development of micro electromechanical systems(MEMS), a pressure sensor fabricated by micro electromechanical elementsis popular in the art.

FIG. 2 shows a package having a pressure sensor according to the priorart, which generally employs an LGA package structure. The packagecomprises a substrate 30, micro electromechanical elements 31 disposedon the substrate 30, sensor film 32 installed on the microelectromechanical elements 31, a cavity chamber 35 formed between thesensor film 32 and micro electromechanical elements, bonding wires 33electrically connected to the substrate 30 and the sensor film 32, a lid34 installed on the substrate 30 that covers the micro electromechanicalelements 31, and an opening 341 formed on the lid 34. Since the lid 34has the opening 341, gas or liquid outside of the lid 34 may enter thelid 34. Further, the cavity chamber 35 also has a constant pressure.Therefore, when an external pressure presses the sensor film 32, apressure difference may exist in the cavity chamber 35, which may bemeasured by the micro electromechanical element 31. The bonding wires 33transmits signals to the substrate 30, and the substrate 30 is disposedon an applicable electronic element. A pressure sensing loop is thusformed. However, since a package in which the micro electromechanicalelement 31 are disposed on the substrate 30 has too great a size, andthe electronic element cannot have a reduced volume.

Consequently, a wafer level micro electromechanical package structureprocess is brought to the art, which uses an etching process to operatea through-silicon via (TSV) process, and performs wafer bonding, so asto reduce the volume of a sensing element. As shown in FIG. 3, whichillustrates a wafer level package having a pressure sensor disclosed inUS Patent Application Publication No. 2006/0185429, the wafer levelpackage comprises a silicon wafer 40, a sensor wafer 41 having a sensorfilm 411 that is stacked on the silicon wafer 40, and a glass wafer 42that is disposed on the sensor wafer 41 by an anodic bonding process.The glass wafer 42 is formed with an opening 421 corresponding inposition to the sensor film 411 together. The silicon wafer 40 and thesensor film 411 form a cavity chamber 45. The wafer level package has asensing principle similar to that of the previously described package,such as further description thereto is hereby omitted. A silicon waferdrilling process is needed to form cavities and blind holes of cavitychamber 45 on the silicon wafer 40. The process is costly and demandssophisticated precision. Therefore, although a pressure sensing elementmay be fabricated by a wafer process, and a package having a smallenough size may be thus obtained, the package is costly because thetechniques for fabricating the same are complicated.

Therefore, how to provide a wafer level package structure fabricated bysimple enough fabrication steps is becoming one of the popular issued inthe art.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems of the prior art, the presentinvention provides a fabrication method for a wafer level package. Thefabrication method includes: preparing a wafer and a lid, the lid havinga metal layer formed on a top surface thereof, the wafer having apressure sensor, comprising a top cavity, electrical connecting padsformed on a circumference of the top cavity, and an etch stop layer anda sensor film formed in the top cavity that are connected to an innerrim of the top cavity, wherein the etch stop layer is positioned betweena bottom of the top cavity and the sensor film; bonding the wafer andthe lid to thereby form a cavity chamber thereinbetween; cutting the lidto expose the electrical connecting pads; electrically connecting themetal layer to the electrical connecting pads via a plurality of bondingwires; forming on the pressure sensor and the metal layer an encapsulantfor encapsulating the bonding wires; removing a portion of theencapsulant from a top surface thereof, so as to expose the bondingwires; forming on the top surface of the encapsulant a redistributionlayer that is electrically connected via the bonding wires to theelectrical connecting pads; and forming from a bottom surface of thepressure sensor a bottom opening for exposing the etch stop layer.

In an embodiment of the present invention, the method further comprisesimplanting solder balls on the redistribution layer.

In an embodiment of the present invention, the method further comprisesinstalling on the pressure sensor a first seal ring that surrounds thetop cavity, and installing on a bottom surface of the lid a second sealring that is correspondingly bonded to the first seal ring. In anembodiment of the present invention, the electrical connecting pads areformed on an external periphery of the first seal ring.

In an embodiment of the present invention, the method further comprises,before the solder balls are implanted, removing the etch stop layer.

The present invention further provides a wafer level package. The waferlevel package includes: a pressure sensor having a top cavity exposedfrom a top surface thereof, and a bottom opening corresponding inposition to the top cavity; a plurality of electrical connecting padsformed on a circumference of the top cavity; a sensor film installedbetween the top cavity and the bottom opening and connected to an innerrim of the top cavity; a lid having a bottom surface bonded to thepressure sensor, to form a cavity chamber thereinbetween; a plurality ofbonding wires electrically connected to the electrical connecting pads;an encapsulant formed on the pressure sensor and the lid thatencapsulates the bonding wires and exposes one end of each of thebonding wires; and a redistribution layer formed on a top surface of theencapsulant and electrically connected to another end of each of thebonding wires.

In an embodiment of the present invention, the wafer level packagefurther comprises solder balls implanted on the redistribution layer.

In an embodiment of the present invention, the wafer level packagefurther comprises an etch stop layer formed under the sensor film.

In an embodiment of the present invention, the wafer level packagefurther comprises a metal layer formed on a top surface of the lid.

In a fabrication method according to the present invention, a waferhaving a pressure sensor is bonded to a lid; electrical connecting padsare formed on the wafer; after the lid is cut, ends of bonding wires areexposed to serve as an electrical connecting path; and a bottom openingis formed on a bottom surface of the wafer so as to form a pressureinlet. Therefore, the present invention integrates wafer coupling andbonding processes, without the need of a through-silicon via (TSV)process that is complicated and costly. A novel wafer level packagehaving a pressure sensor is thus obtained. The method is simple in step,and can fabricate a light, thin, and compact wafer level package.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the followingdetailed description of the preferred embodiments, with reference madeto the accompanying drawings, wherein:

FIGS. 1A to 1H″ illustrate a wafer level package having a pressuresensor and a fabrication method thereof according to the presentinvention, wherein FIG. 1A′ illustrates that a space remains between anetch stop layer and a substrate, FIG. 1H′ illustrates a wafer levelpackage having a pressure sensor that has no etch stop layer, and FIG.1H″ illustrates a wafer level package obtained by the fabrication methodof FIG. 1A′;

FIG. 2 is a cross sectional view of a package having a pressure sensoraccording to the prior art; and

FIG. 3 is a cross sectional view of a wafer level package having apressure sensor package according to the prior art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following illustrative embodiments are provided to illustrate thedisclosure of the present invention, these and other advantages andeffects can be apparently understood by those in the art after readingthe disclosure of this specification. The present invention can also beperformed or applied by other different embodiments. The details of thespecification may be on the basis of different points and applications,and numerous modifications and variations can be devised withoutdeparting from the spirit of the present invention.

Please refer to FIGS. 1A to 1H, which illustrate a wafer level packagehaving a pressure sensor according to the present invention.

As shown in FIG. 1A, a wafer 1 and a lid 2 are prepared. The wafer 1 hasa pressure sensor 10, and the pressure sensor 10 has a top cavity 191,electrical connecting pads 15 formed on a circumference of the topcavity 191, and an etch stop layer 17 and a sensor film 19 installed inthe top cavity 191 and connected to an inner rim of the top cavity 191.The wafer 1 further comprises a substrate 11, and an intermetaldielectric (IMD) layer 13. In an embodiment of the present invention,the substrate 11 and the intermetal dielectric layer 13 are fabricatedby a wafer contract manufacturer, the intermetal dielectric layer 13 isa circuit layer formed by a silicon material, the etch stop layer 17 ismade of silicon dioxide, silicon nitride, or metal, and the sensor film19 is made of silicon, poly-silicon, silicon dioxide, or metal that actsas a pressure sensor. The etch stop layer 17 is interposed between thesubstrate 11 and the sensor film 19. The top cavity 191 is formed on topsurfaces of the intermetal dielectric layer 13 and the sensor film 19.The sensor film 19 is connected to a circuit layer in the intermetaldielectric layer 13. The sensor film 19 may be deformed and transmitelectronic signals via the circuit layer in the intermetal dielectriclayer 13 to the electrical connecting pads 15 on the intermetaldielectric layer 13. In the embodiment shown in FIG. 1A, a bottom cavity211 is formed on a bottom surface of the lid 2, and a metal layer 22 isformed on a top surface of the lid 2. The bottom cavity 211 can beformed by etching the bottom surface of the lid 2 by a dry or wetetching process. The bottom cavity 211 corresponds in size to the topcavity 191.

In another embodiment shown in FIG. 1A′, the etch stop layer 17 is notinstalled on the substrate 11, as shown in FIG. 1A, and a gap or a space171 is formed between the etch stop layer 17 and the substrate 11. Theetch stop layer 17 and the sensor film 19 are still bonded to the innerrim of the intermetal dielectric layer 13, so as to form the top cavity191 on the top surface of the sensor film 19.

As shown in FIG. 1B, the intermetal dielectric layer 13 of the pressuresensor 10 is bonded to the lid 2 by a bonding process, for example, suchthat the top cavity 191 corresponds in position to the bottom cavity 211and forms a sealed cavity chamber 25 between the pressure sensor 10 andthe lid 2. In an embodiment shown in FIG. 1B, a first seal ring 16 isinstalled on the intermetal dielectric layer 13 of the pressure sensor10 that surrounds the top cavity 191, and a second seal ring 26 isformed on the bottom surface of the lid 2 that surrounds the bottomcavity 211 and are correspondingly bonded to the first seal ring 16. Inan embodiment of the present invention, the first seal ring 16 and thesecond seal ring 26 may be made of metal such as tin or other materialsuch as glass frit. The electrical connecting pads 15 are formed on anexternal periphery of the first seal ring 16.

As shown in FIG. 1 c, the lid 2 is cut to expose the electricalconnecting pads 15.

As shown in FIG. 1D, bonding wires 18 are used to electrically connectthe metal layer 22 to the electrical connecting pads 15. Since theelectrical connecting pads 15 are formed on the intermetal dielectriclayer 13, the electrical connecting pads 15 are electrically connectedto the intermetal dielectric layer 13. In an embodiment of the presentinvention, the electrical connecting pads 15 may be bonded to the metallayer 22 by a bonding process. Then, an encapsulant 20 is formed on theintermetal dielectric layer 13 and the metal layer 22 to encapsulate thebonding wires 18.

As shown in FIG. 1E, a portion of a top surface of the encapsulant 20 isremoved by a chemical mechanical polishing process, to expose thebonding wires 18.

As shown in FIG. 1F, a redistribution layer 21 is formed on the topsurface of the encapsulant 20 where a portion of the encapsulant 20 isremoved, and is electrically connected via the bonding wires 18 to theelectrical connecting pads 15.

As shown in FIG. 1G, a portion of the substrate 11 is removed from abottom surface of the wafer 1 by a dry etching process such as a deepreactive ion etching process (DRIE), or a wet etching process using KOH,so as to form a bottom opening 12 that penetrates the substrate 11.Since the etch stop layer 17 may stop the etching process, after thestep is complete, the etch stop layer 17 is exposed. In an embodiment ofthe present invention, the etch stop layer 17 may be removed, dependingon users' demands.

As shown in FIG. 1H, solder balls 23 are implanted on the redistributionlayer 21, and the encapsulant 20 is cut, to obtain a single wafer levelpackage 3 having a pressure sensor according to the present invention.

According to the previously described fabrication method, the presentinvention further provides a wafer level package 3, which includes apressure sensor 10 having a top cavity 191 that is exposed from a topsurface thereof and a bottom opening 12 that corresponds in position tothe top cavity 191; a plurality of electrical connecting pads 15 formedon a circumference of the top cavity 191; and a sensor film 19 installedbetween the top cavity 191 and the bottom opening 12 and connected to aninner rim of the top cavity 191. The pressure sensor 10 comprises thesubstrate 11 and the intermetal dielectric layer 13, wherein theintermetal dielectric layer 13 is formed on the substrate 11, and theelectrical connecting pads 15 are formed on the intermetal dielectriclayer 13.

The wafer level package 3 further comprises the lid 2 having a bottomcavity 211 formed on a bottom surface thereof. The bottom surface of thelid 2 is bonded to the intermetal dielectric layer 13 of the pressuresensor 10, such that the bottom cavity may correspond in position to thetop cavity 191, to form a cavity chamber 25 with the top cavity 191. Aplurality of bonding wires 18 are electrically connected to theelectrical connecting pads 15. An encapsulant 20 is formed on thepressure sensor 10 and the lid 2, to encapsulate the bonding wires 18and expose ends of the bonding wires 18. A redistribution layer 21 isformed on a top surface of the encapsulant 20 and is electricallyconnected to the bonding wires 18. Additionally, solder balls 23 may beimplanted on the redistribution layer 21.

In an embodiment, the wafer level package 3 further comprises a metallayer 22 formed on the top surface of the lid 2.

In an embodiment of the present invention, the wafer level package 3further comprises an etch stop layer 17 formed under the sensor film 19and between the bottom opening 12 and the sensor film 19. In anembodiment of the present invention, the etch stop layer 17 is formed onthe substrate 11.

As in an embodiment shown in FIG. 1H, the first seal ring 16 isinstalled on the intermetal dielectric layer 13 of the pressure sensor10 that surrounds the top cavity 191, and the second seal ring 26 isinstalled on the bottom surface of the lid 2 that surrounds the bottomcavity 211 and are correspondingly bonded to the first seal ring 16. Inan embodiment of the present invention, the first seal ring 16 and thesecond seal ring 26 may be made of metal such as tin or other materialssuch as glass frit. The electrical connecting pads 15 are formed on theexternal periphery of the first seal ring, and are electricallyconnected to the intermetal dielectric layer 13. The wafer level package3 further comprises a metal layer 22 formed on the top surface of thelid 2.

The etch stop layer 17 may be removed during the fabrication of thewafer level package. Accordingly, a wafer level package 3′ having apressure sensor that does not have the etch stop layer 17 is obtained,as shown in FIG. 1H′.

In another embodiment shown in FIG. 1H″, if the wafer 1′ shown in FIG.1A′ is selected, a space 171 is formed between the etch stop layer 17and the substrate 11, but the etch stop layer 17 and the sensor film 19are still bonded to the intermetal dielectric layer 13, so as to form atop cavity 191 on the top surface of the sensor film 19.

In a fabrication method according to the present invention, a waferhaving a pressure sensor is bonded to a lid; electrical connecting padsare formed on the wafer; after the lid is cut, ends of bonding wires areexposed, to serve as an electrical connecting path; and a bottom openingis formed on a bottom surface of the wafer to form a pressure inlet.Therefore, the present invention integrates wafer coupling and bondingprocesses, without the need of a through-silicon via (TSV) process thatis complicated and costly. A novel wafer level package having a pressuresensor is thus obtained. The method has simple steps, and may fabricatea light, thin, and compact wafer level package.

The foregoing descriptions of the detailed embodiments are onlyillustrated to disclose the features and functions of the presentinvention and not restrictive of the scope of the present invention. Itshould be understood to those in the art that all modifications andvariations according to the spirit and principle in the disclosure ofthe present invention should fall within the scope of the appendedclaims.

1. A fabrication method for a wafer level package, the fabricationmethod comprising: preparing a wafer and a lid having a metal layerformed on a top surface thereof, the wafer having a pressure sensorwhich comprises a top cavity, electrical connecting pads formed on acircumference of the top cavity, and an etch stop layer and a sensorfilm formed in the top cavity that are connected to an inner rim of thetop cavity, wherein the etch stop layer is positioned between a bottomof the top cavity and the sensor film; bonding the wafer and the lid tothereby form a cavity chamber thereinbetween; cutting the lid to exposethe electrical connecting pads; electrically connecting the metal layerto the electrical connecting pads via a plurality of bonding wires;forming on the pressure sensor and the metal layer an encapsulant forencapsulating the bonding wires; removing a portion of the encapsulantfrom a top surface thereof, so as to expose the bonding wires; formingon the top surface of the encapsulant a redistribution layer that iselectrically connected via the bonding wires to the electricalconnecting pads; and forming from a bottom surface of the pressuresensor a bottom opening for exposing the etch stop layer.
 2. Thefabrication method of claim 1, further comprising installing on thepressure sensor a first seal ring that surrounds the top cavity, andinstalling on a bottom surface of the lid a second seal ring that iscorrespondingly bonded to the first seal ring.
 3. The fabrication methodof claim 2, wherein the electrical connecting pads are formed on anexternal periphery of the first seal ring.
 4. The fabrication method ofclaim 1, further comprising implanting solder balls on theredistribution layer.
 5. The fabrication method of claim 4, furthercomprising, before the solder balls are implanted, removing the etchstop layer.
 6. The fabrication method of claim 1, wherein the etch stoplayer is made of silicon dioxide, silicon nitride, or metal.
 7. Thefabrication method of claim 1, wherein the sensor film is made ofsilicon, poly-silicon, silicon dioxide, or metal.
 8. The fabricationmethod of claim 1, further comprising forming on a bottom surface of thelid a bottom cavity that corresponds in position to the top cavity, soas to form the cavity chamber together with the top cavity.
 9. A waferlevel package, comprising: a pressure sensor having a top cavity exposedfrom a top surface thereof, and a bottom opening corresponding inposition to the top cavity; a plurality of electrical connecting padsformed on a circumference of the top cavity; a sensor film installedbetween the top cavity and the bottom opening and connected to an innerrim of the top cavity; a lid bonded to the pressure sensor via a bottomsurface of the lid, to thereby form a cavity chamber thereinbetween; aplurality of bonding wires each having one end electrically connectingthe electrical connecting pads; an encapsulant formed on the pressuresensor and the lid for encapsulating the bonding wires, with another endof each of the bonding wires being exposed from a top surface of theencapsulant; and a redistribution layer formed on the top surface of theencapsulant and electrically connected to the another end of each of thebonding wires.
 10. The wafer level package of claim 9, furthercomprising an etch stop layer formed under the sensor film.
 11. Thewafer level package of claim 10, wherein the etch stop layer is made ofsilicon dioxide, silicon nitride, or metal.
 12. The wafer level packageof claim 9, further comprising a first seal ring on the pressure sensorthat surrounds the top cavity, and a second seal ring on a bottomsurface of the lid for being correspondingly bonded to the first sealring.
 13. The wafer level package of claim 12, wherein the electricalconnecting pads are formed on an external periphery of the first sealring.
 14. The wafer level package of claim 9, further comprising a metallayer formed on a top surface of the lid.
 15. The wafer level package ofclaim 9, wherein the sensor film is made of silicon, poly-silicon,silicon dioxide, or metal.
 16. The wafer level package of claim 9,further comprising solder balls implanted on the redistribution layer.17. The wafer level package of claim 9, further comprising a bottomcavity formed on a bottom surface of the lid that corresponds inposition to the top cavity, so as to form the cavity chamber togetherwith the top cavity.